1. Field of the Invention
The invention relates to spill containment techniques for preventing the undesirable discharge of chemical materials onto the ground and, more particularly, to a compact spill containment pan that is disposed at a railroad siding so as to collect any inadvertent spills that may occur during a railroad tank car loading or unloading operation.
2. Description of the Prior Art
Traditionally, railroad tank car loading and unloading has been relatively unregulated. In the past, railroad sidings reflected that lack of concern because they had no provision to collect accidental discharges of whatever was being loaded and unloaded. Often the commodity being shipped was inexpensive or perceived to be of little environmental impact, and therefore any spills were either hosed down or just left for the next rain to clear away. With the advent of stiff fines and high soil remediation costs, techniques to prevent spills or eliminate adverse environmental consequences have become important.
Since spills most often occur during a loading or unloading operation, well-designed spill containment pans can be used to collect and possibly economically reuse spilled chemicals. Some spill containment pans actually are only diversion aprons that require the construction of some type of collection sump. These sumps are subject to crack failure or to filling with dirt and water. Since spill containment pans are exposed to rainwater, snow, and blowing dirt and debris, their effectiveness as spill containment devices is questionable. Environmental regulations provide that any rainwater collected in these spill containment pans is considered to be contaminated and must be handled with the same concern (and at the same cost) as hazardous waste.
Prior efforts to collect leaking, dripping and spilled materials, particularly oily materials, have included providing a flexible plastic drop cloth or sheet which forms a barrier to prevent contact of the chemical material with the ground. The plastic sheet can be either suspended or mounted to the underside of a transport vehicle, as in U.S. Pat. No. 4,936,418, or it can be provided with inflatable or raised edge structures to funnel fluids to a sump or collecting area as described in U.S. Pat. No. 5,099,872. The barrier sheet type containment arrangements generally do not include any means for preventing unwanted ingress of rain, snow, dirt, dust or other environmental contaminants.
Spill pans with convertible lidded structures are known in the art as taught in U.S. Pat. Nos. 5,052,422 and 4,651,887. The latter patent is designed for use between the rails of a railroad siding. The spill pan described in the '887 patent is generally effective for containing spills and drips that fall directly downwardly between the rails. The spill pan in question requires direct overhead placement of the tank car and its discharge opening in order to be in proper position for use. Moreover, the containment apparatus described in the '887 patent does not provide any means for catching and collecting spills occurring outside the rails instead of between them.
An improved spill containment apparatus is disclosed in U.S. Pat. No. 5,435,458, issued Jul. 25, 1995 to Merrill E. Bishop, the disclosure of which is incorporated herein by reference (referred to herein as "the Multi-Pan Patent"). In the Multi-Pan Patent, three separate spill containment pans are disclosed--a center pan disposed between the rails and outboard pans disposed outside each of the rails. The pans have movable covers that prevent dirt or rainwater from entering the pans when the covers are in the closed position. When the covers for the outboard pans are opened, the covers provide additional spill collection surfaces. The cover for the center pan slides longitudinally of the railroad tracks, on special rails, to cover or uncover the center containment pan.
While the apparatus disclosed in the Multi-Pan Patent has proven to be very effective in practice, it employs three pans that are disposed in a fixed location relative to a railroad siding. The pans occupy a considerable amount of ground area in order to carry out their intended function of collecting inadvertent spills. Because the spill containment pans disclosed in the Multi-Pan Patent are well-built, they necessarily are somewhat expensive to manufacture. It is possible that the expense of the pans may serve as an impediment to their widespread purchase and implementation.
Desirably, a spill containment apparatus for use with railroad tank cars would be relatively compact and inexpensive. Any such spill containment apparatus hopefully would be able to be reconfigurated on site to protect an adequate spill-collection area beneath a railroad tank car.